EPA OAR/OAQPS/EMAEMC: OAQPS-18: Gaseous Organic Compounds in Air Emissions by Gas Chromatography
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Official Method Name
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Method 18 - Measurement of Gaseous Organic Compound Emissions by Gas Chromatography |
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Current Revision
| 2000 |
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Media
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AIR |
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Instrumentation
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Gas Chromatograph (Unspecified Detector) |
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Method Subcategory
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Organic |
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Method Source
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Citation
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Brief Method Summary
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The major organic components of a gas mixture are separated by gas chromatography (GC) and individually quantified by flame ionization, photoionization, electron capture, or other appropriate detection principles. The retention times of each separated component are compared with those of known compounds under identical conditions. Therefore, the analyst confirms the identity and approximate concentrations of the organic emission components beforehand. With this information, the analyst then prepares or purchases commercially available standard mixtures to calibrate the GC under conditions identical to those of the samples. The analyst also determines the need for sample dilution to avoid detector saturation, gas stream filtration to eliminate particulate matter, and prevention of moisture condensation. |
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Scope and Application
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This method is designed to measure organics in air emissions from stationary industrial sources. While designed for ppm level sources, some detectors are quite capable of detecting compounds at ambient levels, e.g., ECD, ELCD, and helium ionization detectors. Some other types of detectors are evolving such that the sensitivity and applicability may well be in the ppb range in only a few years. This method will not determine compounds that (1) are polymeric (high molecular weight), (2) can polymerize before analysis, or (3) have very low vapor pressures at stack or instrument conditions. |
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Applicable Concentration Range
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< 1ppm to upper range of instrument |
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Interferences
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(A) Co-elution. Resolution interferences that may occur can be eliminated by appropriate GC column and detector choice or by shifting the retention times through changes in the column flow rate and the use of temperature programming. (B) Contamination. The analytical system is demonstrated to be essentially free from contaminants by periodically analyzing blanks that consist of hydrocarbon-free air or nitrogen. (C) Cross-Contamination. Sample cross-contamination that occurs when high-level and low-level samples or standards are analyzed alternately is best dealt with by thorough purging of the GC sample loop between samples. (D) Water vapor. To assure consistent detector response, calibration gases are contained in dry air. To adjust gaseous organic concentrations when water vapor is present in the sample, water vapor concentrations are determined for those samples, and a correction factor is applied. (E) Run-time. The gas chromatograph run time must be sufficient to clear all eluting peaks from the column before proceeding to the next run (in order to prevent sample carryover). |
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Quality Control Requirements
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(A) Recovery study for direct interface or dilution interface sampling -- This is done to ensure that there are no significant leaks in the sampling system. (B) Recovery study for bag sampling -- This is done to demonstrate that proper sampling/analysis procedures were selected. (C) Recovery study for adsorption tube sampling -- This is done to demonstrate that proper sampling/analysis procedures were selected. |
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Sample Handling
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Detailed sample collection and handling procedures, including sampling train diagrams, are provided in the method. |
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Maximum Holding Time
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Not Available |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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